Two visits to RSA are proposed, the first (11/1/99) to 3/31/00) to achieve aims 1) and 3) listed above in section 18, and the second (7/l/00 to 1/31/01) to pursue aims 2) and 4). The survey done in the 1980's of childhood cancer in Namibia will be updated during visit 1. If the high rate of brain tumors among Herero children persists, the applicant and RSA collaborators will develop a protocol for molecular analysis of tissue blocks from children with brain tumors in the first survey in Namibia. This protocol will be discussed with US colleagues on return to the US between visits. The interval between visits will also allow the applicant to check in on the conduct and progress of her US-based research. Visit 2 will aim to test tribal drinking water, foods and soil for levels of nitrate and nitrite, and, if deemed desirable and feasible, to collect buccal washings from pediatric brain tumor patients and their parents. The sponsor would like guidance during visit 1 in setting up a registry of childhood cancers for Western Cape Province, which he contends can be constituted for the period 1983-1999 by using the two provincial hospital-based registries. During visit 2, after registry data are available for analysis, plans are to investigate the descriptive epidemiology of childhood leukemia, brain cancers and other childhood cancers looking at a number of demographic factors including ethnicity and area of residence (urban versus rural and proximity to the Cape Town nuclear power station), and to initiate further studies as indicated. Aim 5) above will be pursued during both visits.